In semiconductor microfabrication, a resist pattern is formed by a method including: (1) a step of forming a resist film by coating a resist composition on a substrate, and removing a solvent therefrom; (2) a step of pre-baking the resist film; (3) a step of exposing the pre-baked resist film; (4) a step of subjecting the exposed resist film to post-exposure-baking; and (5) a step of developing, by using a liquid developer, the resist film having been subjected to the post-exposure-baking, to form a resist pattern. For example, in Examples of Japanese Laid-Open Patent Publication No. 2006-257078, a chemically amplified photoresist composition comprising a copolymer having a weight-average molecular weight of about 9,200 is described. Hereinafter, “weight-average molecular weight” may be simply referred to as “Mw”.